He pioneered the concept of literate programming. He is considered a famous programmer, known for his geek humor: as examples, he pays a finder's fee of $2.56 for any typos/mistakes discovered in his books because "256 pennies is one hexadecimal dollar". Version numbers of his TeX software approach pi, that is versions increment in the style 3, 3.1, 3.14 and so on, version numbers of Metafont approach e similarly; he once warned users of his software,
"Beware of the above code. I have only proven it correct, not tested it." (source (http://www-cs-faculty.stanford.edu/~knuth/faq))